One of the important subsystems of the two-channel monopulse direction-finding system is the beam-forming network (BFN). Such direction-finding systems use an antenna that is excited in a sum (.SIGMA.) mode and a single complex difference (.DELTA.) mode. It is the task of the beam-forming network to form four beams, two each in the azimuth and elevation planes from the .SIGMA. and .DELTA. modes generated on the antenna. Mathematically, this means that with .SIGMA. and .DELTA. as inputs, the beam-forming network provides .SIGMA.+.DELTA., .SIGMA.-.DELTA., .SIGMA.+j.DELTA., and .SIGMA.-j.DELTA. outputs.
Theoretically, a number of networks are feasible that can perform this function. They might consist of a combinaton of 3-dB quadrature couplers, magic-T's, in-phase power dividers and phase shifters. Not all of these components are necessary to form any one beam-forming network. FIG. 1 shows the simplest of such beam-forming networks and consists of three 3-dB quadrature couplers and one in-phase power divider. FIGS. 2 and 3 show other examples of conventional beam-forming circuits that have been widely applied by Radiation Systems, Inc. as well as other companies. FIG. 4 illustrates a standard product sold by Anaren Microwave, Inc. However, these devices which are illustrated in FIGS. 1 through 4 introduce boresight error dependent on the quality of the individual components, e.g. the amplitude and phase balance thereof.